If a 9.0 earthquake were to strike the Washington coast residents would have 15 to 20 minutes to prepare for a 60-foot-tall wave to hit Long Beach, Westport, Ocean Shores and other coastal communities.
That's according to a newly published Southwest Washington Tsunami Inundation Hazard Map.
The maps, produced by the Washington Geological Survey, model a 2,500-year Cascadia Subduction Zone Earthquake Scenario in the area surrounding Willapa Bay and Grays Harbor using a simulated magnitude 9.0 earthquake.
The Cascadia Subduction Zone is a 600-mile-long rift where two tectonic plates push against each other. It runs from off Vancouver Island to off the Northern California coast.
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"Modeling results indicate that the first tsunami wave is projected to arrive on land along the outer coast in 15 to 20 minutes following the earthquake," Daniel Eungard and the report's other scientists said. "Inundation depths range from 20 to 60 feet on the outer coast, decreasing to generally less than 10 feet within Willapa Bay and Grays Harbor."
The expected speed of the wave could exceed 40 miles per hour, the report said. More than one wave could be expected - up to 12 hours after the initial quake.
Geographical features, tidal effects and other factors limit the map from precisely predicting the effects on specific areas.
"However, this model is an excellent tool for evacuation and recovery planning," the authors said.
Previous studies have shown sudden submergence events hitting Willapa Bay once every 500 to 540 years.
The last major earthquake on the Cascadia subduction zone was about a 9.0 magnitude event in 1700. Waves hit Japan, according to historical records.
Craig Sailor; (253) 597-8541